You can still use defragmentation or clean up tools for a messed up XP, although it won't be as efficient as reinstalling.
If you don't want thps3 to mess up your resolution run it with -windowed, but I don't think anybody's been able to join servers, including
this guy.
I only use windows for thps3 and thug2, I need linux for everything else. BTW
http://en.wikipedia.org/wiki/Linux_gaming, Daimonin's pretty good but it's inactive =< lol.